i don't know where to get exterior shell cases, but my friend sure knows, i might have to go ask him. For the newest custom firmware, it's 3.40OE-A, is the best one and 3.40IE which just has an extra recovery mode, which you most likly don't need.

Ebay, but it's only a faceplate, you cannot change the color of the back. Any attempt to do so, by anyone but an expert would break your psp. So you have to stick with black as the back color cannot be changed.